In the past, several metal oxide-removers have been employed. Some of these removers contained, among other constituents, a metal complexing agent, polyvinylpyrrolidone (PVP), a surfactant, a water-soluble fruit acid, or some combination thereof. However, each of these compositions suffered drawbacks. Many were effective only on a limited variety of metal oxides, and could be used only according to one method. Some required high temperatures for optimum results. Further, many compositions were ineffective on soiled surfaces.
It is well settled that a metal oxide-removing composition should be simple and inexpensive to use. The remover should also be non-toxic and non-irritating when used as intended.